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A number of countries, including the United States, have been planning for long-term storage of nuclear wastes. While many of these nations plan to keep the waste isolated from water, that's not something that can be guaranteed over the extremely long lifespans of the waste. If water reaches the radioactive isotopes, there's the chance that the isotopes could contaminate the groundwater in the area and spread well beyond the site of the storage repository.

To prevent that, plans are to have multiple layers of defense. The waste itself will be incorporated into a chemically inert, insoluble glass. And the glass itself will be placed in a stainless steel flask that will keep it from mixing with the surroundings.

Each of those materials seems to work well in tests. But now, a large team of researchers has found that, in combination, the materials aren't as robust as we'd like them to be. The problems only occur if water somehow gets into the container, but if it does, the interface between the glass and stainless steel actually accelerates chemical reactions that degrade both.

At the interface

The work focuses on what could happen if long-term exposure of the stainless steel flask to water causes sufficient decay to allow water to reach the interior. While some repositories are designed to keep the storage containers dry, it's not clear how successful that will be, since we don't really have the understanding of how changes in things like rainfall can affect groundwater flows on the sorts of time scales the waste has to be protected.

As a result, the planning has included designing materials that should be able to remain stable even if they're exposed to water. And, so far, testing of the stainless steel containers and the waste-containing glass have indicated that it can hold up to extended exposure to water. But the researchers here decided to test what happens when the two materials are brought into contact with each other, as they would be during long-term storage.

In this case, water getting inside of the stainless steel container would percolate into the narrow space between the glass and the steel. And here, there's the possibility of what's apparently termed "crevice corrosion." In the narrow interface between the two materials, the chemistry can be very different than in a bulk solution. Local concentrations of dissolved material can be much higher, material that dissolves on one surface can immediately react with the other, and the chemistry can create feedback loops, greatly increasing the rate of otherwise rare reactions.

In the case of the crevice between the stainless steel and the glass, a lot happens when some of the metals present dissolve. They can drop the local pH, which will then increase the rate at which the stainless steel corrodes. Meanwhile, some of the dissolved metal ions will include some of the radioactive material. To balance the chemistry, the environment outside the crevice will become more basic, which could trigger additional chemical reactions.

Real-world data

That's what can happen. What actually does? To find out, the researchers used a standard (non-radioactive) glass material and stainless steel. These were pressed up against each other, and a solution of sodium chloride was added. The mixture was kept at 90°C for 30 days. The water had dissolved oxygen in it, which would be relevant to the conditions that might take place at the Yucca Mountain repository in the United States; other nations are planning repositories that would have anoxic conditions. At the end of 30 days, the team did some spectroscopic imaging to figure out where various materials ended up.

After 30 days, some of the glass was completely depleted of the metals it normally contains, leaving nothing but silicon behind. That's the typical result of acidic leaching on the glass. Instead, there was a significant amount of iron built up in the area, indicating that the stainless steel was also degrading. In fact, the researchers suggest that the chromium dissolving from the stainless steel enhances the general reactiveness of the environment.

The stainless steel surface itself was covered with a film that was primarily composed of iron and silicon, but also contained aluminum, sodium, and other metals. This implies that at least some of the dissolved material was re-deposited, near where they dissolved. To an extent, the film should reduce the corrosion of the stainless steel over time, but detecting that might require a longer-term experiment.

None of this, obviously, is good news. As the authors state, "this could lead to an enhanced release of radionuclides from this ceramic waste form." Which, obviously, isn't what you'd want from a long-term nuclear waste storage.

This is only a risk if the waste containers are in contact with water long enough to lose some of their integrity. But that's valuable information, given that the risk evaluation involved with choosing waste repositories includes considerations of groundwater exposure. And it very strongly indicates that we have to do more testing of the entire waste-containment system, in addition to testing its individual parts.

206 Reader Comments

Apologies, but whenever this topic comes up, required linking. As an aside, the linked scene from the film bizarrely mostly works as an independent music video. Not sure if intentional on the part of the filmmakers.

In regards to the actual article, glad someone is at least looking into these issues now rather than the seemingly human default of "Today's solutions are tomorrow's problems™".

Temperature is usually a big factor in reaction rate - why'd they pick almost the boiling point of water? Are those vitrified casks generating that much heat?

Higher temperature can usually be used as a proxy for very long time. We can't run 1000 year experiments here, so we turn up the heat.

We've been doing elevated temperature testing as a proxy for extreme lifetime testing for a very long time and it is a well understood engineering technique. For a diffusion-reaction dominated system the formulas for converting temperature to time are well studied.

A number of countries, including the United States, has been planning for long-term storage of nuclear wastes

It's all a moot point until the US gets past a NIMBY mentality. Decades of misinformation, Hollywood liberties in movies, and crap management and lack of R&D spending has lead us to today public fearmongering. No one is going to deny that there isn't inherent risk, and the possibility of a catastrophic disaster. But so is leaving this spent fuel piling up at the individual plants and climate change in 100 years. And yes I would not mind having a storage facility 50-100 from me if its in the middle of a freaking mountain away from major water tables, actively monitored.

Nuclear power makes the most sense when we avoid asking difficult questions such as, "Are we really sure the waste is going to stay put for longer than recorded human civilization has been around?"

And, "Can we build control systems that work correctly under all circumstances without human intervention?" Because if we know one thing about human nature, it's that people are not capable of paying attention to things that are boring for really long periods of time.

Yes, the safety record of nuclear power is actually fairly good compared to the toll taken by toxic fossil fuels. But that's no longer a valid comparison when wind and solar are now cheaper than nuclear. Yes we need to operate the nuclear plants we already have for as long as possible. Yes, we need to figure out economically feasible utility scale electric power storage, but we haven't been at it seriously for all that long, and this could be a solved problem in another decade.

This article potentially confuses vitrified waste storage technology which has been contemplated for various DOD waste streams with spent nuclear fuel storage that Yucca was primarily created for. Presently, I know of no plan to place glass vitrified waste of any kind into SS canisters, in particular spent nuclear power fuel which is by itself quite inert.

But I'm sure many will be happy to allow the assumption that this is about spent nuclear power fuel to go unchecked. Hence the lack of clarification and a misleading big picture of spent nuclear fuel. This study is about high level defense waste disposal.

The study takes one very specific option of many off the table for long term storage of cold war waste.

A note to readers and authors... please make sure you understand which waste you are talking about in the future, and don't trust reporters to get it right.

The business case for grid-scale power generation has largely evaporated, but it's going to be with us for a long time in small doses. I don't foresee the disappearance of the nuclear submarine any time soon. And for as long as we want to make RTGs and nuclear weapons, research and process reactors seem likely to remain with us.

Long-term storage is unnecessary anyways. It just has to be stored long enough that society has advanced to the point of being able to economically process it back into fresh fuel. A century should be plenty long enough considering a century ago we were still flying zeppelins. All this talk of having to store it for thousands or millions of years just plays to environmentalists who want to kneecap nuclear power by making it pay for absurdly expensive storage solutions. And kneecapping nuclear extends the fossil fuel age which it actually could have largely ended 30 years ago.

The business case for grid-scale power generation has largely evaporated, but it's going to be with us for a long time in small doses. I don't foresee the disappearance of the nuclear submarine any time soon. And for as long as we want to make RTGs and nuclear weapons, research and process reactors seem likely to remain with us.

The problem shrinks, but it does not go away.

Grid-scale power is still very much alive. Small-scale wind sucks, putting enough solar+battery in every home is pretty expensive for the foreseeable future, microhydro requires you live in a steep place with a lot of land and rain. Grid-scale everything except transmission is a lot more capital efficient.

Also: another major reason for nuclear reactors: radionuclides for medicine.

Burying items for 10,000 + years is not really a viable solution especially if we end up forgetting the sites we bury them.

The only solutions will be the hardest ones,1. Find alternate power source besides Nuclear Power and invest heavily until we do.2. Find a way to speed up radioactive decay in order to neutralize as much radioactive material as much as possible. While not practical, at one point in time we thought human flight was impractical also. We may not have the necessary science to do so now, but unless we start it is a goal we will never be able to achieve.

We bury all sorts of toxic shit and then plop houses down on it. I vetoed a very nice house my ex wanted, because it was on contaminated land. (The city had tested for oil and found it — indeed you can see the seep — and they hoped you wouldn’t wonder what else they hadn’t tested for.)

Nuclear energy is the cleanest energy! Solar and the others cannot compete. Just look at our wonderful Fukushima resort to get an idea of how clean Nuclear energy is! They will soon be dumping all of their half-filtered water into the ocean. Heating it up most likely too over time as the thing has never stopped spewing radiation.

SO CLEAN AND TASTY. I'd love to force every nuclear apologist to go live in Fukushima and eat the food there. You'd have a lot nuclear apologists shutting the fuck up real fast.

There’s actually nothing scary that you or me would see if we visited Fukushima. The exclusion zone is based on a very cautious radiation cutoff. Inside that zone, I’d expect to see a human-disturbed urban environment gradually giving way to a diverse natural ecosystem as we see in Chernobyl where life is thriving and endangered species have a new lease on life.

In any case, nuclear accidents have damaged like 0.000000001% of our planet. Fossil fuels damage 100%. Anti-nuclear activists, such as yourself, have extended the fossil fuel age by 30 years by making us wait for wind / solar to mature. We’ll see if the planet can handle the 30-50 year wait for magic solar.

Eternal storage has always been a bad idea. At the very least we should be fast breeder reacting this waste into hot short-lived waste that can decay on site in pools.

If you think dealing with nuclear waste is a pain you're going to love dealing with the massive amounts of intermediate level waste that reprocessing generates.

Even if you do manage to burn the fuel to completion, you can't burn up the long lived fission products that pose the greatest long term risk.

You don’t understand the timescales here. Most of the dangerous radioactive stuff in nuclear waste has half lives of decades or centuries. The stuff that lasts for millennia is stuff like plutonium which is useable as fuel. Separating the two created two easily solved problems— stuff that needs to be stored for mere centuries and stuff to put back in the reactor. There’s nothing that needs storing for millennia.